The present invention relates to an improved process for the continuous fermentation of must in a plurality of serially connected fermentation vats to produce wine comprising fermenting the must in the initial fermentation stage in one or more relatively large fermentation vats and completing the fermentation of said must in the final fermentation stage in one or more fermentation vats having a size smaller than that employed in the initial fermentation stage.
Heretofore, in the continuous fermentation of a sugared must to obtain ethanol or wine, a plurality of serially connected fermentation vats, open or closed, being more or less equal in size were employed. The must, comprising the fermentation medium, was continuously introduced into the upper portion of the first fermentation vat wherein the initial fermentation took place. The fermentation medium was then withdrawn from the bottom or lower one-third portion of the first fermentation vat and introduced into the second fermentation vat, of approximately equal size, near the top or upper third portion thereof wherein the fermentation process was continued. This same operating scheme was repeated when more than two serially connected fermentation vats were employed, as was generally the case. Thus, the fermentation medium from the second fermentation vat was withdrawn from the bottom or lower one-third portion thereof and introduced into the third fermentation vat near the top or upper one-third portion thereof, this scheme being repeated until introduction of the fermentation medium into the final fermentation vat where the fermentation process was completed.
Thereafter, the resulting wine or ethanol was separated from the fermentation medium, generally, by centrifugation techniques, the separated wine then being directed to a distillation stage.
Also recovered during this centrifuging operation was a yeast cream stream which was acid treated for a period of time generally about 1 to 3 hours to reduce the pH thereof to about 2 or 3. The acid-treated yeast cream was then recycled to the initial fermentation vat. Thus, at least two treatment vats were required in a conventional continuous fermentation process to produce wine or ethanol, one being employed for the initial treatment operation, the other for completing the process wherein the desired product was withdrawn and a yeast cream, already treated, was recycled to the first of fermentation vat.
However, it has been observed that such a conventional fermentation process as described above exhibits some significant disadvantages. One important disadvantage is that the control of the drop in degrees Brix of the wine being produced from one vat to the next is difficult to follow, this being occasioned by the use of fermentation vats having a more or less equal size.
As a consequence of this, it has been found difficult to select for introduction into the distillation process the optimum fermentation medium, i.e. the medium in a given fermentation vat having the highest alcohol content and the lowest residual reducing sugar level. Also, it has been observed that with the use of equally sized fermentation vats throughout the fermentation process, yeasts or other deposits collect at the bottom of the vats, the fermentation medium retention time in each such equally sized vat being essentially the same for a given batch.
Another disadvantage often associated with a conventional fermentation process as described above is that because of the circulation pattern of the fermentation medium, as more fully described below with reference to FIG. 1, fermentation media having different degrees Brix and therefore different alcohol contents are admixed which can be deleterious to the fermentation process.
Yet another significant disadvantage often experienced in the conventional fermentation process described above results from recycling yeast cream from the final fermentation vat to the initial fermentation vat. This recycled yeast cream generally is expended or significantly weakened due to its prolonged contact with the quantities of alcohol produced in the medium and also with various impurities present in the final fermentation vat from which it is withdrawn.